arXiv subjects

Olav F. Syljuasen

Publications and source records attributed to Olav F. Syljuasen.

23 records · Page 2Linked to original sources

arXiv2002

Anomalous Spin Excitation Spectrum of the Heisenberg Model in a Magnetic Field

Making the assumption that high energy fermions exist in the two dimensional spin-1/2 Heisenberg antiferromagnet we present predictions based on the pi-flux ansatz for the dynamic structure factor when the antiferromagnet is subject to a uniform magnetic field. The main result is the presence of gapped excitations in a momentum region near (pi,pi) with energy lower than that at (pi,pi). This is qualitatively different from spin wave theory predictions and may be tested by experiments or by quantum Monte Carlo.

cond-mat.str-el↗

arXiv2000

Quantum renormalization of high energy excitations in the 2D Heisenberg antiferromagnet

We find using Monte Carlo simulations of the spin-1/2 2D square lattice nearest neighbour quantum Heisenberg antiferromagnet that the high energy peak locations at (pi,0) and (pi/2,pi/2) differ by about 6%, (pi/2,pi/2) being the highest. This is a deviation from linear spin wave theory which predicts equal magnon energies at these points.

cond-mat.str-el↗

arXiv2000

Loop Algorithms for Asymmetric Hamiltonians

Generalized rules for building and flipping clusters in the quantum Monte Carlo loop algorithm are presented for the XXZ-model in a uniform magnetic field along the Z-axis. As is demonstrated for the Heisenberg antiferromagnet it is possible from these rules to select a new algorithm which performs significantly better than the standard loop algorithm in strong magnetic fields at low temperatures.

cond-mat.str-el↗

arXiv1997

Correlation Lengths in Quantum Spin Ladders

Analytic expressions for the correlation length temperature dependences are given for antiferromagnetic spin-1/2 Heisenberg ladders using a finite-size non-linear sigma-model approach. These calculations rely on identifying three successive crossover regimes as a function of temperature. In each of these regimes, precise and controlled approximations are formulated. The analytical results are found to be in excellent agreement with Monte Carlo simulations for the Heisenberg Hamiltonian.

cond-mat.str-el↗

arXiv1996

Gauge invariance of the beta-function in nonrelativistic quantum electrodynamics

Recently there has been much interest in gauge theories applied to condensed matter physics. I show that for a system of nonrelativistic electrons coupled to a U(1) gauge field in the presence of a Fermi surface, the beta-function to one-loop order is, for a particular family of gauge-choices, independent of the gauge-choice.

cond-mat↗